Power over Ethernet refers to a system for distributing power to Ethernet devices through standard Category 5/5e twisted-pair cables currently used to carry Ethernet data. The Ethernet device supplying the power is referred to as Power Sourcing Equipment (PSE) and the Ethernet device receiving the power is referred to as the Powered Device (PD). In accordance with the Institute of Electrical and Electronic Engineers (IEEE) standard reference 802.3af hereby incorporated by reference herein, the PSE first determines, or discovers, whether a connected device is a PoE compliant PD. If so, the PSE transmits direct current power to the PD at 48 volts with a maximum current of 350 milliamperes. As an optional extension to the discovery process, the PD may also specify the amount of power requirements from the PSE. PoE may be used to supply reliable power to low power Ethernet devices including voice over Internet Protocol (VoIP) telephones, wireless access points (WAP), and security cameras, for example.
The IEEE standard reference 802.3af defines types of PSEs including an endspan and midspan. An endspan PSE incorporates the power sourcing functionality within a network switch and the power transmitted via the data channels. That is, DC power is combined with the data signals transmitted on pin-pairs 3 and 6 and pin-pairs 1 and 2 of the Ethernet cable. A midspan PSE is a stand-alone device operatively coupled between the PD and a convention Ethernet switch, for example. The midspan PSE transmits power via unused cable pin-pairs 4 and 5 and pin-pairs 7 and 8. The PDs are generally adapted to receive power from either an endspan PSE or a midspan PSE.
When deployed in a network, a PSE switch may have a combination of PoE compliant PDs and various other non-compliant devices including desktop computers, servers, and printers, for example, which generally require more power than the PSE can provide. In normal operating conditions, the PSE can power each of the connected PDs. Where the public power grid goes down and power to the PSE switch lost, however, the power provided by the PSE to a plurality of PSs may be limited by the power supplied to the PSE switch by an uninterrupted power supply (UPS), for example. If the PSE switch cannot sustain the power requirements of all the PDs, the PSE switch may be forced to choose from among PDs those for which to continue power and those PDs to power down in accordance with a user defined configuration. Contemporary endspan PSE implementations require an operator to manually configure each port's power priority. As such, the operator need necessarily know in advance whether a port is to be coupled to a higher priority VoIP phone or a lower priority data device, for example. This configuration procedure is tedious and requires operator intervention whenever a PD is relocated and the port connection changed. There is therefore a need for a technique to automatically identify a port's power priority and conveniently change the power priority with minimal operator intervention as the devices move around in the network.